The sanctions block all assets of Iran's central bank and other financial institutions

President Barack Obama cites the institutions' "deceptive practices"

Western powers have repeatedly sanctioned Iran over its nuclear program

Washington (CNN) -- The United States has moved to freeze assets of Iran's government and financial institutions, saying they had engaged in "deceptive practices," President Barack Obama's administration announced Monday.

An executive order signed Sunday by Obama freezes all assets of the Iranian government and banks held in the United States, according to John Sullivan, a Treasury Department spokesman.

Previously, recipients of Iranian funds covered by U.S. law were required to "reject" such transactions under sanctions first imposed in 1995, according to the Treasury Department.

"I have determined that additional sanctions are warranted, particularly in light of the deceptive practices of the Central Bank of Iran and other Iranian banks to conceal transactions of sanctioned parties, the deficiencies in Iran's anti-money laundering regime and the weaknesses in its implementation, and the continuing and unacceptable risk posed to the international financial system by Iran's activities," Obama said in a statement to Congress released by the White House.

Iran is under intense international pressure over its nuclear program, which the International Atomic Energy Agency has said may be designed to develop a nuclear weapon.

The new sanctions send Iran the message that "it will face ever-increasing economic and diplomatic pressure until it addresses the international community's well-founded and well-documented concerns regarding the nature of its nuclear program," the U.S. Treasury Department said in a fact sheet on the new sanctions.

Even prior to Monday's sanctions, dozens of Iranian companies, financial institutions and individuals were under Western sanctions related to the nuclear program. The United States has repeatedly sanctioned Iranian banks, companies and individuals over the nuclear program, most recently in January.

Also in January, the European Union announced a prohibition on oil imports from Iran and banned trade in petrochemical equipment and technology, diamonds and precious metals with the Middle Eastern state.

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